Becky/dldt custom build (#4383)
Becky/dldt custom build (#4383)

* set NGRAPH_TAG when no TAG file present

* use default build version with custom-build tag

Co-authored-by: Sang Ik Lee <aa6563a7b56e5ef7f7ffa08e0bc60e65c5df68a1@intel.com>

NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph