Some minor refinements to generic-resource-api

Minor refinements to generic-resource-api including:
1) Replace printStackTrace() with log
2) Use built-in string formatting instead of string concatenation
3) Removed redundant ';' after switch statement
4) Change the private method names to follow guidelines to start with lower case
5) Removed redundant null assignment

Change-Id: I48eb08f7305aa549b952715615201a13c3458ca4
Issue-Id: SDNC-45
Signed-off-by: Gaurav Agrawal <gaurav.agrawal@huawei.com>