Add support for ENV of the form: ENV name=value ...
still supports the old form: ENV name value

Also, fixed an issue with the parser where it would ignore lines
at the end of the Dockerfile that ended with \

Closes #2333

Signed-off-by: Doug Davis <dug@us.ibm.com>
Merge pull request #8251 from duglin/Issue2333

Add support for ENV of the form: ENV name=value ...