Add error handling for when faasd cannot find unit files

Changelog for 0.2.4:

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Install faasd to /usr/local/bin

Changelog for 0.2.3:

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Add arm switch

Changelog for 0.2.2:

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Fix vendoring for go-execute

Changelog for 0.2.1:

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Clean-up on shutdown and run forever

Changelog for 0.2.0:

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Add systemd package and faasd install

Changelog for 0.1.7:

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Update component versions

Changelog for 0.1.6:

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Add async and queue-worker

Changelog for 0.1.5:

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Fix version in Makefile

Changelog for 0.1.4:

• PR #2 Add Travis Build Status Badge by @utsavanand2

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Don't clean-up

Changelog for 0.1.3:

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