Fetching users from LDAP requires creating public ids for them.
id_mapping_api does that. Creating public ids is slow, because it
requires performing N INSERTs for N users, and there is no way to
work around that. It leads to very slow responses to queries like
"list users".
By pre-creating these public ids we improve API users' experience.
Add keystone-manage mapping_populate command that creates id mapping entries
for users.
bp ldap-preprocessing
Partial-Bug: 1582585
Change-Id: I98f795854aee26f9e7f668372c47572d2b6d4f0f
b1fdad9875