Fix miserable performance issues

:Release Notes:
Made cppcheck pass without performance complains

:Detailed Notes:
- useless postfix operations on non-primitive types
- definitely overridden variable value
- assignment of variable value to itself
- bad prefix operation
cppcheck diff:
[Src/BackupManager.cpp]: (performance) Inefficient usage of
    string::find() in condition; string::compare() would be faster.
[Src/BuildInfoHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/BuildInfoHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/EraseHandler.cpp] -> [Src/EraseHandler.cpp:196]: (performance)
    Variable 'ret' is reassigned a value before the old one has been
    used.
[Src/NetworkConnectionListener.cpp] ->
    [Src/NetworkConnectionListener.cpp:122]: (performance) Variable
    'ret' is reassigned a value before the old one has been used.
[Src/PrefsFactory.cpp]: (performance) Prefer prefix ++/-- operators
    for non-primitive types.
[Src/TimePrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/TimePrefsHandler.cpp]: (warning) Redundant assignment of
    'launchStr' to itself.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.
[Src/WallpaperPrefsHandler.cpp]: (performance) Prefer prefix ++/--
    operators for non-primitive types.

:Testing Performed:
desktop build

:QA Notes:

:Issues Addressed:
[ANG-851] LSS: Investigate and fix issues detected by cppcheck

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: I456708234a05af0b355b2b3235060c2de12214f8
Reviewed-on: https://g2g.palm.com/4562
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Andrii Zora <andrii.zora@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>