KNOX-2629 - Fix new shellcheck errors

[zeroflag]

What changes were proposed in this pull request?

With shellcheck v0.7.2 there are some new errors coming when running the build with -Dshellcheck=true.

Most of these aren't real issues. In one case I disabled the warning (SC2153 - possible misspelling), in other cases I had to specify the path of a referenced shell script.

How was this patch tested?

By running the full build with -Dshellcheck=true.

[smolnar82]

LGTM
Thanks, @zeroflag !

[smolnar82]

Thanks, @zeroflag for your contribution. It's a small but very important change!

[smolnar82]

I tried it locally (intentionally made a mistake in knox-functions.sh) and it worked like a charm:

[WARNING] No shellcheck download url provided for current os.name-os.arch [Mac_OS_X-x86_64]
[INFO] shellcheck release will be fetched at [https://github.com/koalaman/shellcheck/releases/download/v0.7.2/shellcheck-v0.7.2.darwin.x86_64.tar.xz]
[WARNING] No signatures were supplied, skipping file validation
[INFO] Got from cache: /Users/sandormolnar/.m2/repository/.cache/download-maven-plugin/shellcheck-v0.7.2.darwin.x86_64.tar.xz_039c1f418e8c8ff4a7ca3beddcbfc3dc
[INFO] Expanding: /Users/sandormolnar/projects/knox/gateway-release-common/target/shellcheck-plugin/shellcheck-v0.7.2.darwin.x86_64.tar.xz into /Users/sandormolnar/projects/knox/gateway-release-common/target/shellcheck-plugin
[WARNING] 
[WARNING] In /Users/sandormolnar/projects/knox/gateway-release-common/home/bin/knox-functions.sh line 57:
[WARNING]   if [ "$JAVA" != "" ]; then;
[WARNING]                             ^-- SC1051: Semicolons directly after 'then' are not allowed. Just remove it.
[WARNING] 
[WARNING] For more information:
[WARNING]   https://www.shellcheck.net/wiki/SC1051 -- Semicolons directly after 'then' ...