log-manager: enable non-standard path for local tests

Enable the log-manager to be launched with a path other than
`/var/phosphor-logging` to allow it to be ran on a development system
for test purp

log-manager: enable non-standard path for local tests

Enable the log-manager to be launched with a path other than
`/var/phosphor-logging` to allow it to be ran on a development system
for test purposes. This required some refactoring throughout as to
how paths were handled.

Tested:

After running tests, `/tmp/phosphor-logging` is populated with
entries. Launching `./builddir/phosphor-log-manager
/tmp/phosphor-logging`, the log-manager will have the entries on
dbus:

```
$ busctl --user tree xyz.openbmc_project.Logging
└─ /xyz
└─ /xyz/openbmc_project
└─ /xyz/openbmc_project/logging
├─ /xyz/openbmc_project/logging/entry
│ ├─ /xyz/openbmc_project/logging/entry/100
│ ├─ /xyz/openbmc_project/logging/entry/101
│ ├─ /xyz/openbmc_project/logging/entry/102
│ ├─ /xyz/openbmc_project/logging/entry/103
```

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I84968edeed0dcf73aaf8bb653060b6d3400b9b7b

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