0.7.0-RC3

[US3030] rafactoring(build script): fix logic for tagging

On branch add-release-tag-script
Changes to be committed:
	modified:   GNUmakefile
	modified:   cstor-container
	modified:   cstor-istgt
	deleted:    cstor-prerequisites

This commit fixes the logic for the tagging. Now it will checkout to
the existing travis-tag (in case it is provided) or use the earlier
logic.

Remove the unused scripts.

Signed-off-by: Utkarsh Mani Tripathi <utkarshmani1997@gmail.com>