[WIP] Enable samba tests without mkdir

[phil-davis]

This is on top of #36422 and is for test confirmation only.

It removes mkdir /var/cache/samba before running the tests. This should make the tests fail, confirming that the mkdir is really required.

[phil-davis]

The tests pass, but there is lots of noise in the test output: https://drone.owncloud.com/owncloud/core/21342/3/10

+ phpdbg -d memory_limit=4096M -rr ./lib/composer/bin/phpunit --configuration tests/phpunit-autotest-external.xml --coverage-clover tests/output/coverage/autotest-external-clover-sqlite-samba.xml apps/files_external/tests/Storage/SmbTest.php
[Welcome to phpdbg, the interactive PHP debugger, v0.5.0]
To get help using phpdbg type "help" and press enter
[Please report bugs to <http://bugs.php.net/report.php>]
PHPUnit 6.5.14 by Sebastian Bergmann and contributors.

Runtime:       PHPDBG 7.1.33-1+ubuntu18.04.1+deb.sury.org+1
Configuration: /drone/src/tests/phpunit-autotest-external.xml

mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
.mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
.mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
.mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
.mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
...
mkdir failed on directory /var/cache/samba: Permission denied
mkdir failed on directory /var/cache/samba: Permission denied
.                                              85 / 85 (100%)

Time: 3.15 seconds, Memory: 30.00MB

OK (85 tests, 383 assertions)

So it is useful to have the mkdir in order to get rid of that "noise" which would really confuse people in future.

[codecov]

Codecov Report

Merging #36425 into master will increase coverage by 0.34%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #36425      +/-   ##
============================================
+ Coverage     64.87%   65.21%   +0.34%     
  Complexity    19792    19792              
============================================
  Files          1271     1208      -63     
  Lines         74723    67304    -7419     
  Branches       1309        0    -1309     
============================================
- Hits          48479    43895    -4584     
+ Misses        25858    23409    -2449     
+ Partials        386        0     -386

Flag	Coverage Δ	Complexity Δ
#javascript	?	?
#phpunit	65.21% <ø> (-0.86%)	19792 <ø> (ø)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Files/Mount/LocalHomeMountProvider.php	0% <0%> (-100%)	1% <0%> (ø)
lib/private/DB/PostgreSqlMigrator.php	0% <0%> (-100%)	6% <0%> (ø)
lib/private/DB/MySQLMigrator.php	0% <0%> (-100%)	5% <0%> (ø)
...ilder/ExpressionBuilder/PgSqlExpressionBuilder.php	0% <0%> (-88.89%)	3% <0%> (ø)
lib/private/Repair/Collation.php	0% <0%> (-87.5%)	12% <0%> (ø)
lib/private/DB/AdapterOCI8.php	0% <0%> (-86.67%)	4% <0%> (ø)
lib/private/DB/AdapterPgSql.php	0% <0%> (-85.72%)	2% <0%> (ø)
...Builder/ExpressionBuilder/OCIExpressionBuilder.php	0% <0%> (-85.19%)	18% <0%> (ø)
lib/private/DB/OracleMigrator.php	0% <0%> (-80.71%)	29% <0%> (ø)
lib/private/Repair/InnoDB.php	0% <0%> (-78.95%)	6% <0%> (ø)
... and 105 more

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