gril: Switch process id to radio user

Switching process id to radio user allows us to connect to rild without
the need to apply a patch for removing the id check in the Android
sources. After connecting to rild, we switch back to root user.

Based on Jolla code (https://github.com/nemomobile-packages/ofono,
commit 87f4764bb3d4af5c65d3fde875dbdc25978cba9d)
Merge pull request #78 from alfonsosanchezbeato/radio-user

gril: Switch process id to radio user
gril: Add parsing of password requests replies
rilmodem: Retrieve available retries from requests

The ril requests for entering password were returning the number of
available retries for some modems. As this is highly device dependent
it was not being properly addressed.
unit: Available password retries tests
Merge pull request #79 from alfonsosanchezbeato/pin-mtk

Parse available retries when entering password
gril: data_call parse error fix/code clean-up

Fixed a parse error when a reply to a REQUEST_SETUP_DATA_CALL was
received with a non-zero status.  When this happens the remaining
settings aren't always populated, thus the code was always logging
a parse error with the returned type ( IP protocol ).  As part of
this fix, the grilreply version of the parsing code was removed,
and now this reply is handled by grilunsol which has similar code
to handle the UNSOL_DATA_CALL_LIST_CHANGED message.  Also modified
the data/voice registration reply parsing to no longer translate radio
technology values to ofono's access/bearer technology constants, this
is now handled by the upper rilmodem atoms.
rilmodem: fix problems with setup data call logic

Change gprs-context's SETUP_DATA_CALL logic to use
the g_ril_unsol_parse_data_call_list() which now properly
handles the case where a non-zero status caused an incorrect
parse failure to be logged.  Also changed the code to use
the correct tech value from the gprs atom when building a
REQUEST_SETUP_DATA_CALL.
unit: move all data_call tests to test-grilunsol.c

Fixed unit tests due to merge of grilreply data_call
parsing code into the grilunsol version that handled
data_call_list change events.  Also re-worked data/voice
registration tests to check RADIO_TECH values as opposed
to the high-level ofono constants.
rilmodem: modify gprs-context event logic

This change makes an instance of gprs-context
only listen for data_call_list messages when
it's primary context has been activated.  It
also adds details to the DBG messages to help
differentiate the different context instances.