Add checks to ensure Masthead provided or downloaded successfully (install_bigfix)

[jgstew]

Affected Files:

• https://github.com/jgstew/tools/blob/master/bash/install_bigfix.sh
• https://github.com/jgstew/tools/blob/master/CMD/install_bigfix.bat

These scripts don't currently validate that the masthead file was either provided or downloaded successfully.

[jgstew]

Currently, if the masthead download fails and one is not provided, then bigfix will get installed without it, which leaves it unfunctional.

The script should instead exit with an error message.

The scripts do handle this currently by exiting with error if the argument for relay FQDN is not given, but that will need to be adjusted once the ability to provide a masthead file instead is included. Also, they do not validate that the masthead file actually downloads even when a relay FQDN is provided, which should be addressed.

[jgstew]

This is a duplicate of this issue: #10

This is now resolved.