[dock] Use IOError in place of FileNotFoundError

FileNotFound is Python 3 only, therefore use its base class
to be compatible with both versions of Python.
7 jobs for fix_file_not_found_unkown_exception in 69 minutes and 32 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #138627
docker
build_linux_27

00:06:00

60.0%
passed #138628
docker
build_linux_36

00:05:37

60.0%
passed #138633
macosx
build_macosx_27

00:08:10

60.0%
passed #138630
macosx
build_macosx_36

00:09:22

60.0%
canceled #138629
macosx
build_macosx_27

00:42:08

 
  Docker
passed #138631
docker-build
docker_linux_27

00:51:57

70.0%
passed #138632
docker-build
docker_linux_36

00:51:08

70.0%