Also update BUILD.txt

This task allows us to rebuild memberuid and memberof attributes throughout the
database. This way we can upgrade from version 0.4 databases that didn't
generate and store memberuid.
The task can be invoked by adding a speaicl named entry to the ldb file.
The entry dn to use is: @MEMBEROF-REBUILD, the entry has no attributes and any
attribute is ignored at present.
The entry will not be stored in the database but will just trigger the task to
execute a rebuild of the memberof and memberuid attributes

In sssd only local is a native mpg domain, and it is forced.
All other providers will have to unroll mpg users into a user/group pair of
entries in the db. This allows the provider to automatically establish if
the remote server provides mpg users w/o possibily conflicting manual
configurations on the client trying to force an mpg behavior where none
is provided.

The special persistent local database retains the original name.
All other backends now have their own cache-NAME.ldb file.

Provides also an upgrade function.

This is part of a set of patches to rewrite sysdb to a hopefully better
API, that will also let use use tevent_req async style calls to manipulate
our cache.

This sysdb_req has always really been a transaction handle and not
a request.

This is part of a set of patches to rewrite transaction support in sysdb to a
hopefully better API, that will also let use use tevent_req async style to
manipulate our cache.

Also unify SYSDB_PW_NAME and SYSDB_GR_NAME in SYSDB_NAME and make it "name"