worker: Make log messages about "cache service unavailable" and "webui not available" consistent

[okurz]

Observation

If I start a worker with CACHEDIRECTORY configured but no cache service started (or when it crashed or failed) and multiple web UIs configured I see recurring info/warn messages about the retrying but no information that the cache service connection is retried, e.g.:

[error] Worker cache not available: Cache service info error: Connection refused
[info] CACHE: caching is enabled, setting up /var/lib/openqa/cache/e13.suse.de
[info] Project dir for host e13.suse.de is /var/lib/openqa/share
[info] CACHE: caching is enabled, setting up /var/lib/openqa/cache/yast-openqa.suse.cz
[info] Project dir for host yast-openqa.suse.cz is /var/lib/openqa/share
[info] Registering with openQA e13.suse.de
[warn] Failed to register at e13.suse.de - connection error: No route to host - trying again in 10 seconds
[info] Registering with openQA yast-openqa.suse.cz
[warn] Failed to register at yast-openqa.suse.cz - connection error: Connection refused - trying again in 10 seconds
[info] Registering with openQA e13.suse.de
[warn] Failed to register at e13.suse.de - connection error: No route to host - trying again in 10 seconds
[info] Registering with openQA yast-openqa.suse.cz
[warn] Failed to register at yast-openqa.suse.cz - connection error: Connection refused - trying again in 10 seconds
[info] Registering with openQA e13.suse.de
[warn] Failed to register at e13.suse.de - connection error: No route to host - trying again in 10 seconds
[info] Registering with openQA yast-openqa.suse.cz
[warn] Failed to register at yast-openqa.suse.cz - connection error: Connection refused - trying again in 10 seconds

Suggestion

Likely in

openQA/lib/OpenQA/Worker.pm

Line 215 in 3a581bf

$self->check_availability unless $current_job;

we can handle a false return value of check_availability to log something like log_info "cache service unavailable, retrying in $timeout"

[okurz]

Fixed by #3646