fix inconsistent i18n log message

An inconsistent example:
    imessage = _("Invalid metadata") + ": %(reason)s"
This is not consistent i18n usage. In most of cases, we use _() for
whole string instead of leaving something out.

More than inconsistent, some text in leaving strings may be not
translated, for example, ':' in English is different '：' in Chinese.

Change-Id: I00e690021c44f1debbe034cc0837a07b292ffd1b
Closes-Bug: #1220813
Remove deprecated assert_() usage

The method assert_() is an alias of assertTrue() and
is deprecated since python 2.7

http://docs.python.org/2/library/unittest.html#deprecated-aliases

This removes all assert_() uses.

Change-Id: I9f55c442cc2416a7aa2dac569d1750f723d95184
Utilizes assertIsNotNone

Using assertTrue and the 'is not' operator to test if an element
is not None is too python2.4. Our unit testing framework supports
assertIsNotNone, included from python 2.7, which was created
for these types of tests.

Change-Id: I25c3f2b144357a3f86625deb8e324d78c20b9ce4
Merge "fix inconsistent i18n log message"
Merge "Remove deprecated assert_() usage"
Merge "Utilizes assertIsNotNone"