Removing warnings reported by cppcheck tool.

Removing warnings reported by cppcheck tool.

[Issue#] LINUXWRT-127
[Problem] Cppcheck reports some warnings.
[Cause] N/A
[Solution] N/A
[Verification] Run cppcheck on wrt-installer (with
--suppress=incorrectStringBooleanError) or check cppcheck.txt generated
by buildbot (ignore warnigs like "A boolean comparison with the string literal
... is always true").
Useful could be installation of rpm on target and checking that is all
right still.

Change-Id: Idf0533e5ef7f1de1f127b3b3fea3418ad34e1680