check for active conda environment (NVIDIA#4970) (NVIDIA#4971)

Signed-off-by: Hainan Xu <hainanx@nvidia.com>

reinstall.sh

@@ -24,7 +24,7 @@ if [ ! -z "${NVIDIA_PYTORCH_VERSION}" ]
 then
   echo 'Installing NeMo in NVIDIA PyTorch container:' ${NVIDIA_PYTORCH_VERSION} 'so will not install numba'
 else
-  if [ -x "$(command -v conda)" ]
+  if [ -n "${CONDA_PREFIX}" ]
   then
     NUMBA_VERSION=0.55
     echo 'Installing numba=='${NUMBA_VERSION}