Test remaining API surface of ProcessBuilder.

 - Expand directory() getter/setter test to cover the null value,
   which is documented as a legal value.
 - refactored the ancient code that called execAndCheckOutput()
   to use checkProcessExecution() instead.
   This also makes it easier to remove streamToStringCallable() and
   and execAndCheckOutput(ProcessBuilder) in a future CL because only
   one usage remains, in OldFileTest.
 - Tests the documented behavior of the environment map throwing
   when the existance of a null or non-String key or value is
   queried.

Test: cts-tradefed run cts -c libcore.java.lang.ProcessBuilderTest

Bug: 27464570
Change-Id: Ic48733a403ab3a67165e2fa022cd42848ca8c1fe
2 files changed