Add support for multiple RPC workers under Metaplugin

Metaplugin needs a fix to support multiple RPC workers properly
because a plugin which supports multiple RPC workers cannot
initialize RPC connections at plugin initialization.

Closes-Bug: #1300570
Change-Id: I584f70abb8969054cd4edc8f914d00f6be930bab
(cherry picked from commit 8fb023ed53aff31f37ebebb94aca4f8e2a188342)
Merge "Add support for multiple RPC workers under Metaplugin" into stable/icehouse