Improve building times of IPU docker image (#14934)

Author: otaj

dockers/base-ipu/Dockerfile

@@ -18,6 +18,7 @@ LABEL maintainer="Lightning-AI <https://github.com/Lightning-AI>"
 
 ARG PYTHON_VERSION=3.9
 ARG CONDA_VERSION=4.9.2
+ARG PYTORCH_VERSION=1.9
 
 SHELL ["/bin/bash", "-c"]
 
@@ -56,13 +57,12 @@ ENV \
 
 COPY environment.yml environment.yml
 
-RUN conda create -y --name $CONDA_ENV python=${PYTHON_VERSION} pytorch=${PYTORCH_VERSION} cudatoolkit=${CUDA_VERSION} -c pytorch && \
-    conda init bash && \
+RUN conda init bash && \
     python -c "import re ; fname = 'environment.yml' ; req = re.sub(r'python>=[\d\.]+', 'python=${PYTHON_VERSION}', open(fname).read()) ; open(fname, 'w').write(req)" && \
-    python -c "import re ; fname = 'environment.yml' ; req = re.sub(r'- pytorch[>=]+[\d\.]+', '# - pytorch=${PYTORCH_VERSION}', open(fname).read()) ; open(fname, 'w').write(req)" && \
+    python -c "import re ; fname = 'environment.yml' ; req = re.sub(r'- pytorch[>=]+[\d\.]+', '- pytorch=${PYTORCH_VERSION}', open(fname).read()) ; open(fname, 'w').write(req)" && \
     python -c "fname = 'environment.yml' ; req = open(fname).readlines() ; open(fname, 'w').writelines([ln for ln in req if not any(n in ln for n in ['pytorch>', 'horovod'])])" && \
     cat environment.yml && \
-    conda env update --file environment.yml && \
+    conda env create -f environment.yml && \
     conda clean -ya && \
     rm environment.yml