Do not place empty HTTP_PROXY in env

[dgeo]

Just test for non-emptiness before making it available to exec and upgrade processes

fix #7

[coveralls]

Pull Request Test Coverage Report for Build 9319894713

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 3 of 9 (33.33%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 8.197%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
iocage_lib/ioc_exec.py	3	6	50.0%
iocage_lib/ioc_upgrade.py	0	3	0.0%

Totals
Change from base Build 9317671310:	0.02%
Covered Lines:	799
Relevant Lines:	7754

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💛 - Coveralls