Make PGO backwards compatible with older crunchy-postgres-exporter im…

…ages.

internal/pgmonitor/exporter.go

@@ -122,6 +122,17 @@ func GenerateDefaultExporterQueries(ctx context.Context, cluster *v1beta1.Postgr
 // the source queries files.
 func ExporterStartCommand(commandFlags []string) []string {
 	script := strings.Join([]string{
+		// Check to see if the postgres_exporter command is successful. If it is, we are
+		// using an image that has the command on the PATH. If it isn't, we have an older
+		// image that does not have it on the PATH and we should find the directory that
+		// holds the postgres_exporter binary and add it to the PATH.
+		`rc=0`,
+		`postgres_exporter --version || rc=$?`,
+		`if [ $rc -ne 0 ]; then`,
+		`	dir=$(find /opt/cpm/bin/postgres_exporter* -type d)`,
+		`	export PATH=$PATH:$dir`,
+		`fi`,
+
 		// Set up temporary file to hold postgres_exporter process id
 		`POSTGRES_EXPORTER_PIDFILE=/tmp/postgres_exporter.pid`,