Fix numpy not found issue when installing (Qiskit#1056)

When doing python ./setup.py install in a clean env, CMake is unable to
find numpy. Here we force the installation of numpy if it is not
installed before CMake is called.

Co-authored-by: Christopher J. Wood <cjwood@us.ibm.com>

pyproject.toml

@@ -1,2 +1,3 @@
 [build-system]
-requires = ["setuptools", "wheel", "urllib3<1.26", "conan>=1.22.2", "scikit-build", "cmake!=3.17.1,!=3.17.0", "ninja", "pybind11>2.4", "Cython>0.27.1"]
+requires = ["setuptools", "wheel", "urllib3<1.26", "conan>=1.22.2", "scikit-build", 
+  "cmake!=3.17.1,!=3.17.0", "ninja", "pybind11>2.4", "numpy>1.16.3"]

qiskit/providers/aer/library/save_amplitudes2 copy.py

@@ -0,0 +1 @@
+                 conditional=False):

setup.py

@@ -42,6 +42,11 @@
 except ImportError:
     subprocess.call([sys.executable, '-m', 'pip', 'install', 'pybind11>=2.4'])
 
+try:
+    from numpy import array
+except ImportError:
+    subprocess.call([sys.executable, '-m', 'pip', 'install', 'numpy>=1.16.3'])
+
 from skbuild import setup