32394618, 36899165, 37245921 Fix unread and text_only flags

* Update the TelephonyProvider's backup/restore agent to set the
default "read" flag as 1, or has-been-read. When restoring an mms,
set the text_only flag appropriately. Finally, back up the text in
all mms messages, even if the text is part of a message that contains
an attachment.

Test: updated the unit tests.

Bug: 32394618
Bug: 36899165
Bug: 37245921
Change-Id: If5197b22fd0558764dd1c379d720915e9c38e8b7
2 files changed