Follow changes on slaplib

Mocking slaplib is good, duplicating all its codebase is wrong.
Should use either a simple mockup, or the real slaplib.
More generic code supporting alternative implementations of slaplib

i.e support mocking of slaplib in tests.
Also document about weird behavior of slaplib.
Adapt slapproxy to new slaplib behavior

Fix 428e9dad72e79ae8c396f6b50cd0b3f13b0f202d.
Add test in slapproxy: correct behavior of setting/getting connection parameters.
Simplify condition.

Readability.
Don't send useless attributes.
Send slave_instance_list as well with the instance.
slapproxy tests: Remove getPartitionInformation and update cases.

getFullComputerInformation is basically useless now. We directly get
the information when doing request() & co.
This is NOT related to binary cache, and has nothing to do here.
Move getStatus() interface to be more clear.

Also explicitely state that this is not to be confused with getState().
Add/fix slapproxy tests about request()
Add _instance_guid when doing 'request()' in slapproxy.
Add XXX.