Fix the __validate_instconfig method in the combine_query module to accept more than two entries

Currently, if instconfig is composed of more than two components delimited with the same characters (e.g. sensor_CEADASE_CPHM-500_LP1_PG8_SG2250_STgroundVel,sensor_Nanometrics_Trillium120QA_SG1203_LP120_STgroundVel,sensor_Streckeisen_STS-2_EG3_SG1500_LP120_STgroundVel), this method will discard everything between the first and last components (the above string gives instconfig=sensor_CEADASE_CPHM-500_LP1_PG8_SG2250_STgroundVel,sensor_Streckeisen_STS-2_EG3_SG1500_LP120_STgroundVel).