More granular exit codes

[dagonzalezfo]

#4426 This PR will provide a basic set of error codes for EB. The included ones can be classified in 2 groups

• Eb proper codes:
  • 3: Missing easyconfig
  • 4: No specific easyblock
  • 5: Failed to import easyblock
  • 6: Failed to import class from easyblock
  • 7: No recipe for dependency (robot)
  • 8: Os dependency missing
  • 9: Unavailable sources
  • 10: Sanity check folder/file
  • 11: Can not write module at modules path
  • 12: Validate errors (this is more focus on syntax)
• Other error codes:
  • HTTP: Errors for fetching sources
  • system error codes for system calls
  • LMOD: Errors for loading module