Better MDM push certificate lifecycle

[np5]

• Create MDM push certificate with only a private key
• Upload the certificate later
• CSR download
• Store signed CSR in the Push Certificate
• Signed CSR download

[coveralls]

Pull Request Test Coverage Report for Build 8542093497

Details

• 84 of 109 (77.06%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 78.462%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
zentral/contrib/mdm/forms.py	42	46	91.3%
zentral/contrib/mdm/management/commands/mdmcerts.py	0	21	0.0%
<!--	Total:	84	109	77.06%	-->

Totals
Change from base Build 8486120073:	0.01%
Covered Lines:	35534
Relevant Lines:	45288

---

💛 - Coveralls