fix(hostsensormanager): stop matching decoy release files as os-release (#904)

getOsReleaseFile scans /etc for anything ending in "os-release" to find
the file to read. Problem is centos-release, redhat-release, and similar
distro-specific files also end in that string, so on RHEL-family hosts
readdirnames could hand back one of those instead depending on directory
order, and we'd parse a single free-text line as if it were the
standard KEY=VALUE os-release format.

Switched to an exact filename match since we're only ever looking for
one specific file anyway.

Signed-off-by: Akanksha Trehun <akankshatrehun@gmail.com>