Replaced std::unique_lock with std::lock_quard.
Replaced std::unique_lock with std::lock_quard.

[Issue#]        N/A
[Bug]           N/A
[Cause]         lock_quard is simpler and security-server does not used
                additional benefits from unique_lock.
[Solution]      N/A

[Verification]  Build, run ss tests

Change-Id: I91c626760c13b58e7909752252c86892815fadd7

Samsung/security-manager,pohly/security-manager,pohly/security-manager,pohly/security-manager,Samsung/security-manager,Samsung/security-manager