bintray.sh potential errors creating new packages

[ryane]

It looks like the bintray.sh might have some issues creating packages that don't already exist. I tried to use the script as is in https://github.com/asteris-llc/mantl-private-packaging and ran into problems. The check to determine if the pkg exists used the versioned name ($PKG) instead of the base name ($PKG_NAME). Also, the PKG_METADATA variable did not seem to be properly quoted and the vars were included literally in the JSON and resulted in a bintray api error. This looks like it occurred here for example:

https://travis-ci.org/asteris-llc/mantl-packaging/builds/133152641#L353

In that example, it looks like the script tried to create the package even though it already existed in Bintray because of the check using $PKG instead of $PKG_NAME as described above.

Here is the version I am using in the private repo which appears to work correctly: https://github.com/asteris-llc/mantl-private-packaging/blob/master/scripts/bintray.sh

[langston-barrett]

In general, shellcheck is great for avoiding quoting errors in shell scripts (and many other issues).