Fix gril const todo

This pull request fixes a longtime set of TODOs in the gril unit tests.  It required a change across most of the functions defined in grilreply and grilunsol; changing the ril_message parameters to 'const'.

Built this branch merged with master + the ubuntu master branch ( lp:~phablet-team/ofono/ubuntu ) on x86 and armhf builds, all unit tests pass.

Also ran basic sanity check on mako running trusty touch image #10.