rustpkg: Make test_rustpkg_test_output more permissive

test output may contain color codes, so check for several small strings
instead of one big one.
auto merge of #9640 : catamorphism/rust/rustpkg-test-fix, r=alexcrichton

r? @alexcrichton test output may contain color codes, so check for several small strings
instead of one big one.
Prevent leakage of fmt! into the compiler

We're not outright removing fmt! just yet, but this prevents it from leaking
into the compiler further (it's still turned on by default for all other code).
std: Remove usage of fmt!
extra: Remove usage of fmt!
syntax: Remove usage of fmt!
rustc: Remove usage of fmt!
rusti: Remove usage of fmt!
rustdoc: Remove usage of fmt!
rustpkg: Remove uses of fmt!
compiletest: Remove usage of fmt!
rpass: Remove usage of fmt!
cfail: Remove usage of fmt!
rfail: Remove usage of fmt!
bench: Remove usage of fmt!
tutorial: Remove usage of fmt!
pretty: Remove usage of fmt!