[BUG] Environment variables are overwritten

[raydouglass]

Each docker exec runs with the host's environment variables. This can cause weird issues since things like the PATH is overwritten and the image being used may rely on its specific PATH.

At the very least, PATH from the host should not be used. Potentially nothing from the host should be.

[ajschmidt8]

I'm thinking we should handle environment variables like this:

• Include a checkbox that, when enabled, will automatically pass through all known Jenkins environment variables (we'll have to make a list of all known environment variables provided by Jenkins)
• Include a text area input box for additional environment variables that should be passed into container
  • Input should accept two formats:
    • ENV_VAR, which copies the ENV_VAR from the host machine if it exists, otherwise defaults to blank (i.e. ENV_VAR=)
    • ENV_VAR=value, which lets users explictly pass environment variables with values