CoberturaInstrumentMojo doesn't use maxmem setting

[nomis]

The configuration used for instrumentation creates a new ConfigInstrumentation but doesn't call setMaxmem() on it, so the default 64m applies.

If this is not enough memory for the instrumentation phase then the report generation will fail.

The only way to provide a maxmem setting is via the MAVEN_OPTS environment variable, but it should be possible to do this using the cobertura.maxmem property.