New features for `bootimage runner`

[phil-opp]

Changelog:

• Pass additional arguments to the run command (e.g. QEMU)
• Consider all binaries in the target/deps folder as test executables
• Apply test-timeout config key when running tests in bootimage runner
• Don't apply run-args for test executables
• Add a new test-args config key for test arguments
• Add a new test-success-exit-code config key for interpreting an exit code as success
  • This is useful when the isa-debug-exit QEMU device is used.
• Improve printing of the run command (print string instead of array, print non-canonicalized executable path, respect --quiet)

[phil-opp]

Published as version 0.7.2