NXDRIVE-2135: Check for proxy instantiation success when using a PAC

[BoboTiG]

Also set a lower logging level on proxy validation error to prevent Sentry events spam.

[nuxeojenkins]

View issue in JIRA: NXDRIVE-2135: Check for proxy instanciation success when using a PAC

[sourcery-ai]

Sourcery Code Quality Report (beta)

Merging this PR leaves code quality unchanged.

Quality metrics	Before	After	Change
Complexity	1.94	1.95	0.01 🔴
Method Length	42.73	42.81	0.08 🔴
Quality	8.87	8.87	0.00

Other metrics	Before	After	Change
Lines	990	993	3

Changed files	Quality Before	Quality After	Quality Change
nxdrive/manager.py	8.85	8.85	0.00
nxdrive/client/proxy.py	8.95	8.94	-0.01 🔴

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Overall	Recommendation
nxdrive/manager.py	Manager.__init__	26	443.49	2.73	Split out functionality
nxdrive/manager.py	Manager.bind_engine	15	229.86	4.46	Split out functionality
nxdrive/client/proxy.py	load_proxy	16	142.77	5.39	Split out functionality
nxdrive/manager.py	Manager.get_server_login_type	8	144.83	6.11	Split out functionality

Please see our documentation here for details on how these metrics are calculated.

We are actively working on this report - lots more documentation and extra metrics to come!

Let us know what you think of it by mentioning @sourcery-ai in a comment.