Java: fixing isolation mounts for Alpine musl.

Thanks to @wujjpp.

This closes #490 PR on GitHub.

auto/modules/java

@@ -313,7 +313,7 @@ NXT_JAVA_LIBJVM="$NXT_JAVA_LIB_SERVER_PATH/libjvm.so"
 if [ "$NXT_SYSTEM" = "Darwin" ]; then
 NXT_JAVA_LIBC_DIR="/usr/lib"
 else
-NXT_JAVA_LIBC_DIR=`ldd "$NXT_JAVA_LIBJVM" | grep libc.so | cut -d' ' -f3`
+NXT_JAVA_LIBC_DIR=`ldd "$NXT_JAVA_LIBJVM" | grep -F libc. | cut -d' ' -f3`
 NXT_JAVA_LIBC_DIR=`dirname $NXT_JAVA_LIBC_DIR`
 fi