Fixed Maven plugin not working without install phase.

Fixed Maven plugin not working without install phase.

Fixed small typo, which broke YANG Maven plugin,
when project sources was compiled without install
phase and YANG models were loaded from other artefact
in same build reactor.

[ERROR] yang-to-sources: Unable to parse yang files from /Users/repenno/Documents/sfc-ut3/sfc-provider/src/main/yang
java.io.FileNotFoundException:
/Users/repenno/Documents/sfc-ut3/sfc-model/target/classes (Is a directory)
	at java.io.FileInputStream.open(Native Method)
	at java.io.FileInputStream.<init>(FileInputStream.java:146)
	at
org.opendaylight.yangtools.yang.parser.util.NamedFileInputStream.<init>(Nam
edFileInputStream.java:18)
	at
org.opendaylight.yangtools.yang2sources.plugin.YangSourceFromFile.openStrea
m(YangSourceFromFile.java:27)
	at
org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.toStr
eamsWithoutDuplicates(YangToSourcesProcessor.java:197)

Change-Id: Ia0b7d68dd3c0102134e5425a0705044e92fa0386
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>