test/lvol: start rewriting python tests to bash

There are multiple things wrong with current python tests:
 * they don't stop the execution on error
 * the output makes it difficult to understand what really
   happened inside the test
 * there is no easy way to reproduce a failure if there
   is one (besides running the same test script again)
 * they currently suffer from intermittent failures and
   there's no-one there to fix them
 * they stand out from the rest of spdk tests, which are
   written in bash

So we rewrite those tests to bash. They will use rpc.py
daemon to send RPC commands, so they won't take any more
time to run than python tests.

The tests are going to be split them into a few different
categories:
 * clones
 * snapshots
 * thin provisioning
 * tasting
 * renaming
 * resizing
 * all the dumb ones - construct, destruct, etc

Each file is a standalone test script, with common utility
functions located in test/lvol/common.sh. Each file tests
a single, specific feature, but under multiple conditions.
Each test case is implemented as a separate function, so
if you touch only one lvol feature, you can run only one
test script, and if e.g. only a later test case notoriously
breaks, you can comment out all the previous test case
invocations (up to ~10 lines) and focus only on that
failing one.

The new tests don't correspond 1:1 to the old python ones
- they now cover more. Whenever there was a negative test
to check if creating lvs on inexistent bdev failed, we'll
now also create a dummy bdev beforehand, so that lvs will
have more opportunity to do something it should not.
Some other test cases were squashed. A few negative tests
required a lot of setup just to try doing something
illegal and see if spdk crashed. We'll now do those illegal
operations in a single test case, giving lvol lib more
opportunity to break. Even if illegal operation did not
cause any segfault, is the lvolstore/lvol still usable?
E.g. if we try to create an lvol on an lvs that doesn't
have enough free clusters and it fails as expected, will
it be still possible to create a valid lvol afterwards?

Besides sending various RPC commands and checking their
return code, we'll also parse and compare various fields
in JSON RPC output from get_lvol_stores or get_bdevs RPC.
We'll use inline jq calls for that. Whenever something's
off, it will be clear which RPC returned invalid values
and what were the expected values even without having
detailed error prints.

The tests are designed to be as easy as possible to debug
whenever something goes wrong.

This patch removes one test case from python tests and
adds a corresponding test into the new test/lvol/lvol2.sh
file. The script will be renamed to just lvol.sh after
the existing lvol.sh (which starts all python tests) is
finally removed.

As for the bash script itself - each test case is run
through a run_test() function which verifies there were
no lvolstores, lvols, or bdevs left after the test case
has finished. Inside the particular tests we will still
check if the lvolstore removal at the end was successful,
but that's because we want to make sure it's gone e.g even
before we remove the underlying lvs' base bdev.

Change-Id: Iaa2bb656233e1c9f0c35093f190ac26c39e78623
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Signed-off-by: Pawel Kaminski <pawelx.kaminski@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/459517


Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Broadcom SPDK FC-NVMe CI <spdk-ci.pdl@broadcom.com>