test: suppress certain leaks reported by LSan

test: suppress certain leaks reported by LSan

so we can run TEST-46 under sanitizers once again.

`systemd-homed` runs fsck on home directories, which reports a memory
leak we're not interested in. Let's introduce an LSan suppression file
to get around this. Since the patterns in the suppression file are
matched using basic substring match[0], they're a bit cumbersome, but
should get the work one.

[0] https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer#suppressions

Example leaks (as reported by TEST-46):
```
systemd-homed[1333]: =================================================================
systemd-homed[1333]: ==1333==ERROR: LeakSanitizer: detected memory leaks
systemd-homed[1333]: Direct leak of 24 byte(s) in 1 object(s) allocated from:
systemd-homed[1333]:     #0 0x7f0c8facccd1 in calloc (/usr/lib/clang/12.0.1/lib/linux/libclang_rt.asan-x86_64.so+0xf4cd1)
systemd-homed[1333]:     #1 0x558d9494ff67  (/usr/bin/fsck+0x3f67)
systemd-homed[1333]: Direct leak of 6 byte(s) in 1 object(s) allocated from:
systemd-homed[1333]:     #0 0x7f0c8fa906c1 in strdup (/usr/lib/clang/12.0.1/lib/linux/libclang_rt.asan-x86_64.so+0xb86c1)
systemd-homed[1333]:     #1 0x558d949518fd  (/usr/bin/fsck+0x58fd)
systemd-homed[1333]: SUMMARY: AddressSanitizer: 30 byte(s) leaked in 2 allocation(s).
systemd-homed[1337]: ==1337==WARNING: Symbolizer was blocked from starting itself!
systemd-homed[1337]: =================================================================
systemd-homed[1337]: ==1337==ERROR: LeakSanitizer: detected memory leaks
systemd-homed[1337]: Direct leak of 67584 byte(s) in 1 object(s) allocated from:
systemd-homed[1337]:     #0 0x7f01edb84b19  (/usr/lib/clang/12.0.1/lib/linux/libclang_rt.asan-x86_64.so+0xf4b19)
systemd-homed[1337]:     #1 0x7f01e8326829  (/usr/bin/../lib/libLLVM-12.so+0xb46829)
systemd-homed[1337]: SUMMARY: AddressSanitizer: 67584 byte(s) leaked in 1 allocation(s).
```

With the suppression file:
```
systemd-homed[1339]: -----------------------------------------------------
systemd-homed[1339]: Suppressions used:
systemd-homed[1339]:   count      bytes template
systemd-homed[1339]:       2         30 /bin/fsck$
systemd-homed[1339]: -----------------------------------------------------
systemd-homed[1343]: ==1343==WARNING: Symbolizer was blocked from starting itself!
systemd-homed[1343]: -----------------------------------------------------
systemd-homed[1343]: Suppressions used:
systemd-homed[1343]:   count      bytes template
systemd-homed[1343]:       1      67584 /lib/libLLVM
systemd-homed[1343]: -----------------------------------------------------
```