code refactor: log function

[elenaterenzi]

DoD:

• log function to be placed in common.sh script that takes a string as an input and echoes to stderr the string.
• replace calls to echo with the new log function in all other bash scripts whenever the echo command is logging info to the user
• do not replace calls to echo when it is returning a value (like in createPipeline function for example)
• verify xtrace option still works as expected