al-Wali and al-Mawla are names of Allah, but it is permissible to call a Muslim “mawlana”

Firstly: 

al-Wali and
al-Mawla are two of the names of Allah, because Allah, may He be exalted,
says (interpretation of the meaning): 

“Or have
they taken (for worship) Awliya (guardians, supporters, helpers, protectors,
etc.) besides Him? But Allah, He Alone is the Wali (Protector, etc.). And it
is He Who gives life to the dead, and He is Able to do all things”

[ash-Shoora
42:9]

“Allah is
the Wali (Protector or Guardian) of those who believe. He brings them out
from darkness into light”

[al-Baqarah
2:257]

“And if
they turn away, then know that Allah is your Mawla (Patron, Lord, Protector
and Supporter, etc.), (what) an Excellent Mawla, and (what) an Excellent
Helper!”

[al-Anfaal
8:40]

“Pardon us
and grant us Forgiveness. Have mercy on us. You are our Mawla (Patron,
Supporter and Protector, etc.) and give us victory over the disbelieving
people”

[al-Baqarah
2:286]

“Say:
Nothing shall ever happen to us except what Allah has ordained for us. He is
our Mawla (Lord, Helper and Protector).” And in Allah let the believers put
their trust”

[at-Tawbah
9:51]. 

And the
Prophet (blessings and peace of Allah be upon him) said:

“You
are its Guardian (Wali) and its Lord (Mawla).”

Narrated by
Muslim, 7081 

See: Fayd
al-Qadeer, 2/613; al-Qawaa’id al-Mathla, p. 15 

Secondly: 

It is
permissible to call another person “mawlana” if he is Muslim, but it is not
permissible to say that to a disbeliever. 

Some of the
scholars said that it is permissible to use the word mawla to refer to a
Muslim who is distinguished in knowledge or righteousness. 

The Prophet
(blessings and peace of Allah be upon him) said to Zayd ibn Haarithah: “You
are our brother and our mawla.”

Narrated by
al-Bukhaari, 2552 

The word mawla
may be used with reference to an owner, companion, relative, neighbour,
ally, supporter, lover, benefactor, recipient of kindness, slave or freed
slave. See: al-Qamoos al-Muheet. 

Ibn al-Atheer
said: The word mawla appears frequently in hadeeth. It is a word that may be
applied to many things. It may refer to the Lord, the owner, the master, the
benefactor, the freed slave, the supporter, the lover, the follower, the
neighbour, the cousin, the ally, the son-in-law, the slave, the freed slave,
and the recipient of kindness. It mostly appears in hadeeth and should be
interpreted according to the context of the hadeeth in which it is
mentioned. Everyone who is in charge of a matter or undertakes a matter may
be described as its mawla or wali.

End quote from
an-Nihaayah fi Ghareeb al-Hadeeth, 5/227 

Hence there is
nothing wrong with giving this name to a person so long as he is not a
disbeliever. 

Ibn al-Qayyim
(may Allah have mercy on him) said: Section: The dhimmi cannot be addressed
as Sayyiduna etc 

With regard to
addressing (the dhimmi) as sayyiduna, mawlana and the like (titles roughly
meaning “our master”), that is definitely haraam.

End quote from
Ahkaam Ahl adh-Dhimmah, 2/771 

An-Nawawi
said: Imam Abu Ja‘far an-Nahhaas said in his book Sinaa‘at al-Kitaab: With
regard to the word al-mawla, we do not know of any difference of opinion
among the scholars concerning the fact that no one should say “mawlaya (my
master)” to another person. But I say: We have seen in the previous chapter
that it is permissible in all cases to say mawlaya and there is no
difference between (the two forms of the word). an-Nahhaas was speaking of
the word with the definite article (al-mawla). Similarly, an-Nahhaas said:
The word sayyid may be said to anyone who is not an evildoer, but it should
not be used with the definite article (as-sayyid) to refer to anyone other
than Allah, may He be exalted. But the more correct view is that there is
nothing wrong with saying al-mawla and as-sayyid (with the definite article,
with reference to people) subject to the conditions mentioned above, i.e., a
person may becalled as-sayyid (with the definite article) if he is a person
of virtue and goodness, either because of his knowledge or his righteousness
and so on. If he is an evildoer or there is some doubt concerning his
religious commitment and the like, it is makrooh to call him sayyid.

End quote from
al-Adhkaar, p. 840. See also Mu‘jam al-Manaahi al-Lafziyyah,
p. 535

And Allah
knows best.