[Libguestfs] [PATCH v2 nbdkit 0/5] tests: Move common functions into tests/functions.sh

[Richard W.M. Jones]

v1 was here:
https://www.redhat.com/archives/libguestfs/2018-September/msg00057.html

v2:

 - Fix tab vs spaces in configure.ac.

 - To generate list of plugins, use printf instead of xargs.

 - Use 'source ./functions.sh' instead of 'source functions'.

 - functions.sh: Consistent quoting in foreach_plugin function.

 - functions.sh: Change the contract of start_nbdkit so it requires
   (and checks that) the first two parameters are '-P pidfile'.  This
   avoids needing to iterate over the arguments.

 - functions.sh: Use {1..10} instead of seq.

 - functions.sh: Add a common mechanism for handling traps / cleanups
   (this is extra patch 4/5).

 - functions.sh: start_nbdkit manages its own cleanup function for
   killing nbdkit on exit