gssapi/krb5: delete_sec_context must close ccache if CLOSE_CCACHE
_gsskrb5_init_sec_context() when called with GSS_C_NO_CREDENTIAL
opens the default ccache and sets the CLOSE_CCACHE flag indicating
that the ccache lifetime is tied to the gsskrb5_ctx. When
_gsskrb5_delete_sec_context() is called, it must close the ccache
if the CLOSE_CCACHE flag is set. Otherwise, the ccache resources
will leak.
Leaked since
39fe446983c0e70a0d11b8824684ad912c8e2206.
Change-Id: I8d0faab1e844d68fe71b11b715f8d88fcd2f4af7