Improve LDAP performances when updating records, especially when many user entries exists

[zamentur]

The problem

With 150 users and 12 apps, a yunohost user create take 1min
With 350 users and ~25 apps, a yunohost user create take hours maybe days.

Solution

Replace ldap.modlist.modifyModlist by an optimize code that work for yunohost.

Test in a dev platforme (with ssd 600Mbps) : the 169th user creation is made in ~3s.

PR Status

Need more test to be sure it doesn't break something...

How to test

for i in {1..150}; do echo $i; yunohost user test$i -d ynh.local -F "test test" -p "Thisisadummypa:ssw0rd"; done

[Salamandar]

Not sure about your last commits on [user] -> user, but apart from that, LGTM.