Catch and ignore coverage exceptions on GetCapabilities

[Bang Pham Huu]

It seems that occasionally GetCapabilities in petascope fails to return anything because of trouble in some coverage.

It happened twice to me so far, once because of a bug with gdal transform, now a second time because some coverage is somehow missing.

In both times the only way for me to make petascope and wcst_import usable again was to drop petascopedb and create it again.

I think when reading each coverage information while handling the
GetCapabilities request, if it fails to read / throws an exception - petascope should catch any such exception and log a warning. Then still continue reading the remaining coverages so at least something useful can be returned.