Allow generating different RAPI resource lookup tables

Until now the RAPI resource table returned by
“rapi.connector.GetHandlers” always uses fixed strings or compiled
regular expressions as dictionary keys. Now that a table of all RAPI
resources (and their access rights) should be written for the
documentation, a plain string version of the URIs must be available. The
compiled pattern might contain escape sequences and is not suitable.

This patch changes “GetHandlers” to accept a hook function which is used
to translate non-static resource URIs such as “/2/jobs/[job_id]/wait”.
The default implemention retains the original behaviour by translating
to compiled regular expressions.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>