Pass force_write on FullUpdates

[kozl]

Hi! Thank you for this very useful tool. I suppose, I found a bug.
Steps to reproduce it:

1. No entries in source (LDAP in my case)
2. Full update with force flag (nsscache --config-file=/etc/nsscache.conf update --full --force-write)
3. Even with force-write flag provided it can't update cache because of an empty map

I looked in source code and found that force_flag doesn't get passed into WriteMap function.

[google-cla]

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[kozl]

Signed the Google CLA

[jaqx0r]

Thanks for this! I'd love to see some test coverage for trying to do a full update with an empty source map.

[kozl]

Done

[jaqx0r]

Thanks!

[jaqx0r]

Can you please yapf-format the new tests, and then looks good to go!

[kozl]

✅

[github-actions]

Unit Test Results

    1 files  ±0      1 suites  ±0   2s ⏱️ -1s
294 tests +1  283 ✔️ +2  11 💤  - 1  0 ❌ ±0 

Results for commit babb138. ± Comparison against base commit ff14b97.