Add shell utitily functions for scripts

Add two shell libaries with utilities to write shell scripts.

The 'utils/shlog' file provides macro names for ANSI escape sequences to
control color output on terminals, a 'log' functions with pre-defined
behavior for ERROR, WARN, DEBUG, INFO and SUCCESS level messages, and
the 'quiet' function which executes a command and hides its output.

The 'utils/shfun' file provides an interruptinon handler for SIGINT, and
the following functions:

- run_if_exists: run a command if it is available
- cleanup: cleanup environment, possibly stopping a container and a
  Python virtual environment.
- start_virtual_environmnt: initiates a Python virtual environment
- in_python_virtualenv: test if the script is running inside a Python
  virtual environment
- die: abort the script with an error message end exit code 1

New files:

  - utils/shlog
  - utils/shfun