Fix RuleBuilder remoteable actions running in the local pool.

This CL fixes a bug with RuleBuilder's handling of remoteable actions.
It adds a new type of pool to identify remoteable rules by the android
module context. The pool is then set to nil to actually run actions at
NINJA_REMOTE_NUM_JOBS parallelism.

Test: built aosp crosshatch userdebug
Change-Id: I29452f6fc7a161b94189731e3e3cc1f34907b80c