decode stdout/stderr from run_command (SOFTWARE-5451)

[edquist]

by default Popen.communicate() returns bytes objects, which are printed in a few places - and show up in the logs as b'...', which is especially annoying due to all the escaped internal newlines.

@matyasselmeci - would you prefer encoding="latin1" or anything? I think that would make the prints print garbage if there is actual utf8 data in stdout/stderr, though I know sometimes you like to guard against stray bits.

[matyasselmeci]

__run_command should never raise an error so either use encoding="latin1" or add errors="surrogateescape" or something...