om bosh-env should be able to un-set vars

[kcboyle]

Reference: #385 for more context

In order to make om a better command line tool, it would be nice to be able to easily un-set all vars set by om bosh-env. This makes it easier for users to know that their environment is clean (the biggest use case for this is the headache associated with using a traditional bosh-login when env vars are (silently) set).

Proposed addition to the om bosh-env command:

om bosh-env --unset

Please discuss if this seems unreasonable. Thank you for the proposal @aegershman!

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[iplay88keys]

This isn't possible directly as written since om bosh-env just outputs a list of export commands as it cannot affect the environment of its parent shell.

$ om bosh-env
export BOSH_ENVIRONMENT: example.com
export BOSH_CLIENT: some-client
export BOSH_CLIENT_SECRET: some-client-secret
⋮

As a result, it must be called as: eval "$(om bosh-env)" in order for the environment variables to be persisted after the command has completed.

However, if the unset flag outputted the following:

$ om bosh-env --unset
unset BOSH_ENVIRONMENT
unset BOSH_CLIENT
unset BOSH_CLIENT_SECRET
⋮

We would be able to remove the environment variables by calling: eval "$(om bosh-env --unset)"

[xyloman]

I am a fan of this approach. This might have been stated before but a flag for just Bosh or just credhub env vars would be an added plus.

[iplay88keys]

@kcboyle Any issue with my picking this up and submitting a PR?

[kcboyle]

None at all! We'd appreciate a PR @iplay88keys