Extensions to security_server_open_for function.

Extensions to security_server_open_for function.

Base function extended by new argument 'reader_label':

* int security_server_sharedfile_open(const char *filename, const char *reader_label, int *fd);

Introduced two new functions:

* int security_server_sharedfile_reopen(const char *filename, int *fd);
* int security_server_sharedfile_delete(const char *filename);

[Issue#]        SSDWSSP-398
[Bug/Feature]   New SS API functions.
[Cause]         *open_for* needed more security.
[Solution]      Added new functions.
[Verification]  Build and run new tests:
                security-server-tests-server --output=text --regexp='open_for'

Change-Id: I00dcf1c24c4a2186942b2dff4511e6667a6c5188