Fix installation error when conda enviroment already exists (#81)

ERROR: Could not install packages due to an EnvironmentError: [WinError 5] Access is denied: 'C:\\Users\\ninhu\\AppData\\Local\\CONTIN~1\\MINICO~1\\envs\\r-azureml\\Lib\\site-packages\\_cffi_backend.cp36-win_amd64.pyd'
Consider using the `--user` option or check the permissions.

R/install.R

@@ -22,17 +22,21 @@ install_azureml <- function(version = NULL,
     stop("Anaconda not installed or not in system path.")
   }
 
-  # create conda environment if missing
+  # remove conda environment if already exists
   envs <- reticulate::conda_list()
   if (envname %in% envs$name) {
-    msg <- paste("Using existing environment: ", envname)
+    msg <- sprintf(paste("Environment \"%s\" already exists.", 
+                         "Remove the environment..."),
+                   envname)
     message(msg)
-  } else {
-    msg <- paste("Creating environment: ", envname)
-    message(msg)
-    py_version <- paste("python=", conda_python_version, sep = "")
-    reticulate::conda_create(envname, packages = py_version)
-  }
+    reticulate::conda_remove(envname)
+  } 
+
+  # create conda environment
+  msg <- paste("Creating environment: ", envname)
+  message(msg)
+  py_version <- paste("python=", conda_python_version, sep = "")
+  reticulate::conda_create(envname, packages = py_version)
 
   # install packages
   reticulate::py_install(