Merge remote-tracking branch 'remotes/cschoenebeck/tags/pull-9p-20201102' into staging

Merge remote-tracking branch 'remotes/cschoenebeck/tags/pull-9p-20201102' into staging

9pfs: only test case changes this time

* Fix occasional test failures with parallel tests.

* Fix coverity error in test code.

* Avoid error when auto removing test directory if it disappeared
  for some reason.

* Refactor: Rename functions to make top-level test functions fs_*()
  easily distinguishable from utility test functions do_*().

* Refactor: Drop unnecessary function arguments in utility test
  functions.

* More test cases using the 9pfs 'local' filesystem driver backend,
  namely for the following 9p requests: Tunlinkat, Tlcreate, Tsymlink
  and Tlink.

# gpg: Signature made Mon 02 Nov 2020 09:31:35 GMT
# gpg:                using RSA key 96D8D110CF7AF8084F88590134C2B58765A47395
# gpg:                issuer "qemu_oss@crudebyte.com"
# gpg: Good signature from "Christian Schoenebeck <qemu_oss@crudebyte.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: ECAB 1A45 4014 1413 BA38  4926 30DB 47C3 A012 D5F4
#      Subkey fingerprint: 96D8 D110 CF7A F808 4F88  5901 34C2 B587 65A4 7395

* remotes/cschoenebeck/tags/pull-9p-20201102:
  tests/9pfs: add local Tunlinkat hard link test
  tests/9pfs: add local Tlink test
  tests/9pfs: add local Tunlinkat symlink test
  tests/9pfs: add local Tsymlink test
  tests/9pfs: add local Tunlinkat file test
  tests/9pfs: add local Tlcreate test
  tests/9pfs: add local Tunlinkat directory test
  tests/9pfs: simplify do_mkdir()
  tests/9pfs: Turn fs_mkdir() into a helper
  tests/9pfs: Turn fs_readdir_split() into a helper
  tests/9pfs: Factor out do_attach() helper
  tests/9pfs: Set alloc in fs_create_dir()
  tests/9pfs: Factor out do_version() helper
  tests/9pfs: Force removing of local 9pfs test directory
  tests/9pfs: fix coverity error in create_local_test_dir()
  tests/9pfs: fix test dir for parallel tests
  tests/9pfs: make create/remove test dir public

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>