Better error messaging for mksurfdata_esmf when conda not loaded...

### Brief summary of bug

When a conda environment isn't loaded the error message when running

``` shell
cd tools/mksurfdata_esmf
make all
```
should be improved. This also means the same thing for the underlying python scripts in
tools/mksurfdata_esmf.

### General bug information

**CTSM version you are using:** alpha-ctsm5.2.mksrf.27_ctsm5.1.dev176 (and will be ctsm5.2.0)
**Does this bug cause significantly incorrect results in the model's science?** No

**Configurations affected:** python scripts associated with mksurfdata_esmf

### Details of bug

### Important output or errors that show the problem

```
make all
/glade/derecho/scratch/erik/alpha-ctsm5.2.mksrf.27_ctsm5.1.dev176/tools/mksurfdata_esmf/../site_and_regional/subset_data point --silent --overwrite --uniform-snowpack --cap-saturation --crop --outdir . --include-nonveg --create-surface --lat -7 --lon -55 --site 1x1_brazil
Traceback (most recent call last):
File "/glade/derecho/scratch/erik/alpha-ctsm5.2.mksrf.27_ctsm5.1.dev176/tools/mksurfdata_esmf/../site_and_regional/subset_data", line 34, in
from ctsm.subset_data import main
File "/glade/derecho/scratch/erik/alpha-ctsm5.2.mksrf.27_ctsm5.1.dev176/tools/site_and_regional/../../python/ctsm/subset_data.py", line 65, in
from ctsm.site_and_regional.base_case import DatmFiles
File "/glade/derecho/scratch/erik/alpha-ctsm5.2.mksrf.27_ctsm5.1.dev176/tools/site_and_regional/../../python/ctsm/site_and_regional/base_case.py", line 17, in
import numpy as np
ModuleNotFoundError: No module named 'numpy'
make: *** [Makefile:160: 1x1_brazil-present] Error 1
```