Auto merge of #3509 - froydnj:colored-shell-tests, r=alexcrichton
Auto merge of #3509 - froydnj:colored-shell-tests, r=alexcrichton

disable color shell tests for terminals that don't support color

Some terminals (e.g. running a shell inside Emacs's shell-mode) don't
support color, and running tests that assume the terminal supports color
don't work so well.  Instead, if color is expected, check the terminal
for whether it supports color or not, and act accordingly.

vojtechkral/cargo,achanda/cargo,achanda/cargo,durka/cargo,sbeckeriv/cargo,tshepang/cargo,rust-lang/cargo,tshepang/cargo,sbeckeriv/cargo,eminence/cargo,rust-lang/cargo,achanda/cargo,achanda/cargo,eminence/cargo,vojtechkral/cargo,nipunn1313/cargo,nipunn1313/cargo,tsurai/cargo,vojtechkral/cargo,durka/cargo,rust-lang/cargo,sbeckeriv/cargo,rustyhorde/cargo,rust-lang/cargo,tsurai/cargo,eminence/cargo,rustyhorde/cargo,rustyhorde/cargo,tshepang/cargo,nipunn1313/cargo,tsurai/cargo,sbeckeriv/cargo,vojtechkral/cargo,tsurai/cargo,tsurai/cargo,durka/cargo,durka/cargo,nipunn1313/cargo,tshepang/cargo,eminence/cargo,rustyhorde/cargo