Test if /dev/tty can be opened before reading it

[gabyx]

Better implementation as suggested from #85. The prompt needs to be shown because of the tests and I would leave it like this...

[coveralls]

Pull Request Test Coverage Report for Build 561

• 1 of 2 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 87.154%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
base-template.sh	1	2	50.0%
<!--	Total:	1	2	50.0%	-->

Totals
Change from base Build 557:	-0.04%
Covered Lines:	1954
Relevant Lines:	2242

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💛 - Coveralls

[rycus86]

Thanks a lot!