Correct tests due to change in Security Server password validity calculation

Correct tests due to change in Security Server password validity calculation

[Issue#]       SSDWSSP-332
[Bug]          Two tests fails after correction in Security Server
[Cause]        Test cases tc10 and tc18 use UINT_MAX as a value of valid_days
               for password setting. This value is now rejected by SS pwd,
               because it causes overflow when changing number of days to
               seconds.
[Solution]     Checking if UINT_MAX is correctly rejected when trying to set pwd
               Added calculation of proper max number of valid days that will
               not cause unsigned int overflow while changing to seconds.
[Varification] Build and run tests.

Change-Id: I25139243d11eba4eb58e79db0fc3b869eedb26e6