Better share group testing

[nickvergessen]

• Step1 fix the names to be more descriptive
• Step2 fix the order (so we dont share user1 > user3 > user2, but 1 > 2 > 3)
• Step3 compare the md5 to the one of the group sharee, to make sure the file is uploaded correctly, (which it is not in owncloud's current master, see https://github.com/owncloud/core/issues/17188 + https://github.com/owncloud/core/pull/17191 )
• Step4 use methods instead of doing the compare manually

For easier review have a look at the individual commits, the second commit is still odd, but I just switched the two def sections and replaced user2 with user3 and the otherway around.

@moscicki

[nickvergessen]

@moscicki mind having a look of review on my 3 PRs?