Catch device creation exceptions in test_device_instantiation

[callumforrester]

Fixes #850

Instructions to reviewer on how to test:

1. Run unit tests
2. Break a device and confirm tests fail

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[callumforrester]

Unsurprisingly, since these tests have been swallowing exceptions for 5 months, there are now previously hidden errors that we need to decide what to do about. Most of them seem to revolve around /dls_sw not being available in the CI environment, which I think is fair, our device instantiation tests should be able to run without it. For one thing, it is down right now.

It appears this wasn't a problem previously because fake_with_ophyd_sim=True was being used to create fake ophyd device classes via ophyd.sim.make_fake_device, which strips out all of the logic from the ophyd device class and essentially makes a mock. Now many of those devices have been migrated to ophyd-async, whose mock feature only affects signal backends, not the logic in the class constructor/methods.

One fix I thought of was to make sure that /dls_sw is not accessed in any of the device constructors or connect methods, in which case test_device_instantation.py and dodal connect -s would never touch it, but I am open to alternatives. Tagging @DominicOram, @DiamondJoseph and @noemifrisina for opinions.